Streamflow of 2013 - Water Year Summary

Introduction

The maps and graphs in this summary describe
streamflow conditions for water-year 2013 (October 1, 2012 to September 30,
2013) in the context of the 84-year period 1930-2013, unless otherwise noted.
The illustrations are based on observed data from the U.S. Geological
Survey's (USGS) National Streamflow Information Program (http://water.usgs.gov/nsip). The period 1930-2013
was used because prior to 1930, the number of streamgages was too small to
provide representative data for computing statistics for most regions of the
country.

In the summary, reference is made to the term "runoff," which is
the depth to which a river basin, State, or other geographic area would be
covered with water if all the streamflow within the area during a specified time period was uniformly distributed upon it. Runoff quantifies the magnitude of water
flowing through the Nation's rivers and streams in measurement units that can
be compared from one area to another.

Each of the maps and graphs below can be expanded to a larger view by
clicking on the image. In all the graphics, a rank of 1 indicates the highest
flow of all years analyzed.

National Overview

Average runoff in the Nation’s rivers and streams during water-year 2013
(9.21 inches) was very close to the long-term annual mean for the
United States (9.30 inches). Nationwide, 2013 streamflow ranked 48th out of the 84 years in the period 1930-2014. Note that in previous water-year summaries (prior to 2011) the median runoff, not the average runoff, was compared among time periods.

Regional Patterns

The United States (including Puerto Rico) is divided into 21 large
drainages, or water resources regions. These hydrologic areas are
based on surface topography and contain either the drainage area of
a major river, such as the Columbia, the combined drainage areas of
a series of rivers, such as the Texas-Gulf region which includes a
number of rivers draining into the Gulf of Mexico, or the area of
an island or island group. Water resources regions provide a coherent,
watershed-based framework for depicting streamflow variations.

Streamflows at much-below normal levels were reported in the Alaska, Texas Gulf, Great Basin, and Upper Colorado regions. Below normal conditions were measured in the Rio Grande and Hawaii regions. Much-above normal streamflow was reported in the Tennessee region. Above normal streamflow occurred in the Upper Mississippi region.

Seasonal Characteristics

Autumn season (October-December) streamflow was at record low levels (ranking 84th in 84 years) in Arizona. Much-below and below normal flows were reported in central, southwestern, and southeastern states: Georgia, South Carolina, Colorado, Oklahoma, Texas, Kansas, Minnesota, Nebraska, Missouri, Arkansas, Wisconsin, Iowa , New Mexico, Utah, Illinois, North Carolina, and Wyoming. Hawaii and Alaska also were at much-below and below normal levels. Above normal flows were reported in Washington, Oregon, California, South Dakota, Delaware, and Maryland. Nationwide, autumn season streamflow ranked 55th out of 84 years.

* For Puerto Rico, 70 years of available data were used.

Winter season (January-March) streamflow was at record low levels in Nebraska and Alaska. Much-below and below normal flows were reported in California, Oregon, Idaho, Nevada, Utah, Wyoming, Colorado, New Mexico, Texas, Oklahoma, Missouri, North Dakota, Minnesota, Wisconsin, and Puerto Rico. Above normal streamflow was only reported in Mississippi and Maine. Nationwide, winter season streamflow ranked 66th out of 84 years.

*For Puerto Rico, 70 years of available data were used.

Spring season (April-June) streamflow was below or much-below normal in Texas, New Mexico, Arizona, Colorado, Utah, Nevada, California, Oregon, Idaho, Wyoming, and Alaska. Above and much-above normal streamflow was seen in central northern and some east coast states: North Dakota, Minnesota, Wisconsin, Michigan, Iowa, Illinois, Indiana, Missouri, Tennessee, Mississippi, North Carolina, Virginia, Delaware, and Connecticut. Nationwide, spring season streamflow ranked 33th out of 84 years.

*For Puerto Rico, 70 years of available data were used.

Summer season (July-September) streamflow in eastern and southeastern states, as well as a few middle western states, was above or much-above normal. South Carolina was at record high level. Streamflow was below or much-below normal in Montana, Idaho, Nebraska, Texas, Louisiana, and Alaska. Nationwide, summer season streamflow ranked 8th out of 84 years.

*For Puerto Rico, 70 years of available data were used.

High and Low Flows

In any given month, on average, it is expected that five percent of the streamgages will experience very high (>95th percentile) and very low (<5th percentile) average streamflow. During water-year 2013, five spring and summer months (April, June, July, August, and September) had a greater than expected percentage of streamgages reporting very high streamflow (6, 10, 12, 6, and 6 percent, respectively). In contrast, there were 5 months (from November to April except January) with a greater than expected percentage of streamgages with very low flows (9, 7, 6, 8, and 6 percent, respectively).

The bankfull streamflow is defined as the highest daily mean streamflow value expected to occur, on average, once in every 2.3 years. In 2013, 46 percent of streamgages had a daily mean streamflow value above the bankfull level. This value is slightly higher than the expected number (43 percent) to occur in any given year. Since 1950, the largest number of streamgages reporting higher than bankfull streamflow in any one year was 69 percent, which occurred in 1996.

The 10th percentile 7-day low flow is defined as the lowest 7-day average streamflow expected to occur, on average, once in every 10 years. In water-year 2013, 7 percent of the streamgages reported a 7-day low flow less than the 10th percentile 7-day low flow value. The expected number to occur in any given year is 10 percent. Since 1950, the largest percentage of streamgages reporting a 7-day low flow less than the 10th percentile 7-day low flow was 25 percent, which occurred in 1954.

Additional Information

The USGS operates a network of nearly 8,000 streamgages nationwide,
most in real-time. Current information derived from these stations
is available on the web at http://waterwatch.usgs.gov.
Tables of data that summarize historical streamflow conditions by
State, beginning in the year 1900, can be accessed at http://waterwatch.usgs.gov/?m=statesum.
These tables are updated every few months to reflect the most current
streamflow data.

The streamflow information used to prepare this summary is also used
for water management, monitoring floods and droughts, bridge design,
and for many recreational activities. To obtain real-time and archived
streamflow data and information, visit http://water.usgs.gov/nwis.
Although the national streamgage network is operated primarily by
the USGS, it is funded by a partnership of 850 agencies at the Federal,
State, tribal, and local levels, and USGS National Streamflow Information Program
(http://water.usgs.gov/nsip/) and the USGS Cooperative Water
Program (https://water.usgs.gov/coop/about/monitors.html).